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5 Signs You May Be Dehydrated

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Working out hard under the hot sun? Watch for these warning signs that your body’s too low on H20.

by
Hollis Templeton 1 / 6

Nothing screams summer like a good sweat under the hot sun, but if you’re not replacing fluid as fast as your body’s pumping it out of your pores, your outdoor workout could be cut short by sluggishness, cramped muscles or even life-threatening heat illness. How do you know if you’re in danger? We asked Douglas Casa, PhD, an exertional heat stroke expert and chief operating officer at the University of Connecticut’s Korey Stringer Institute, to pinpoint five dehydration symptoms to watch for when exercising al fresco.

1. You're extra thirsty

A dry mouth doesn’t automatically mean danger. But thirst is your body’s way of reminding you to reach for your water bottle when you’re on your way to becoming dehydrated, so don’t ignore the obvious. According to the Institute of Medicine, men should take in approximately three liters (about 13 cups) of liquid a day—but that’s just a baseline. If you’re exercising in hot and humid weather, you’ll need to fill up on more fluid. Sick of plain ol’ H20? Keep in mind that water-dense fruits and vegetables, like celery, cucumbers, and melon, also help with hydration.

2. You’re dizzy or fatigued

If you feel a rush of lightheadedness when you stand up quickly after sitting down to stretch, it’s a good sign that your body’s low on H20. Dizziness is caused by a decrease in blood flow to the brain. And when there’s not enough water in your blood, blood volume and pressure both drop.

What about feeling run-down? Well, virtually every cell in the body needs water to function, so when you’re lacking liquid, your body has to work extra hard to carry about basic functions, hence the reason finishing that last mile or rep feels almost impossible.

3. Your heart rate is out of whack

Caught your breath, but heart still racing? When dehydration decreases the volume of blood in your body, your heart speeds up as it attempts to pump out the same amount of blood it would if you were properly hydrated. (In other words, when you’re dehydrated, your heart's hard at work maintaining your blood pressure.) If you’re extremely dehydrated and your heart really gets going (say, above 100 beats per minute), you may experience palpitations, which are essentially hiccups in your heart’s rhythm.

4. Your muscles are cramping

Ever notice that you get more muscle cramps during the summer months? When you get super sweaty during a workout, you’re not just pumping water out of your pores; your body’s also flushing out electrolytes likes sodium and potassium. Electrolytes are essential to proper muscle and nerve function, and when they’re off balance, it’s easy to end up with cramp or muscle spasm after exercise.

5. Your urine is almost orange

One of the easiest ways to tell if you’re dehydrated: take a peek at your pee before you flush. If you’re properly hydrated, your urine will be clear or very light yellow. But when you’re dehydrated, your kidneys try to keep every last drop of water in your body and thus decrease the amount of pee that you produce. And the less water that your body has to flush out, the less water there is in your urine, and the more concentrated (read: darker) it becomes.